Igor Aranson
Argonne National Laboratories
Densely packed granular assemblies under shear undergo a first order phase transition: from static they become fluidized and the flow ensues. At smaller values of the shear stress, the granular ``fluid'' freezes, and the flow terminates. We developed a novel approach to dense shear granular flows. Our approach is based on the hydrodynamic equation of momentum conservation combined with phenomenological Ginzburg-Landau type equations for the order parameter at the first order phase transition from granular solid to fluid. In this context the order parameter describes the degree of fluidization of granular flow. Our framework correctly captured the shape of avalanches, transitions from triangular to up-hill avalanches, flow velocity distributions and even time-dependent stick-slips in granular layers. We calibrated our phenomenological model with large-scale Molecular Dynamics simulations.